Field effect transistors (FETs) introduced with mechanical stress applied to a channel region have enhanced speed performance. In some approaches, in an FET, stressor material with a lattice constant different from that of a channel region is grown in a source region and a drain region. Lattice mismatch between material of the channel region and the stressor material causes mechanical stress applied to the channel region, thereby increasing carrier mobility in the channel region and the driving capability of the FET.
However, accompanying with the use of the stressor material, a leakage current of the FET when the FET is in an OFF state is increased. For example, stressor material such as SiGe adopted in a p-channel FET has a narrower bandgap than material such as Si in a body region of the FET. Therefore, junction leakage is increased due to band-to-band tunneling. Such increase in leakage current in a dynamic cell, such as a dynamic random access memory cell, adversely impacts data retention performance.
Like reference symbols in the various drawings indicate like elements.